How do I prevent people from 'leeching' my images?

Many people have expressed concern that other users have tried to 'steal' or 'leech' their images, simply by referencing them in their own HTML pages. For example, you can easily put the following line of code into your own pages, hosted anywhere: 
 

<IMG SRC=http://www.aspfaq.com/img/nld.jpg>

 
And of course my logo will show up on your page. 
 
Here is one way to get around this, making it easy for you to host all of your images and not worry about others being able to 'borrow' them. Place your image file(s) in a folder, either in an unknown spot in your webroot or outside of your webroot altogether, and then use the following code (which plops c:\okay.gif into the browser if the request came from the same domain, otherwise it returns c:\warning.gif - which can be as effective as you make it in having people tear down their references to your image(s)): 
 

<%      ref = lcase(Request.ServerVariables("HTTP_REFERER"))      if instr(ref, lcase("YOUR_DOMAIN_NAME"))>0 then          fn = "okay.gif"       else          fn = "warning.gif"      end if        FPath = "c:\" & fn       Set adoStream = CreateObject("ADODB.Stream")       adoStream.Open()       adoStream.Type = 1       adoStream.LoadFromFile(FPath)       Response.BinaryWrite adoStream.Read()       adoStream.Close: Set adoStream = Nothing       Response.End   %>

 
Then simply reference this ASP file in your other pages: 
 

<IMG SRC=imageFile.asp>

 
You may want to add other clauses for other domains your site may be referenced as, such as localhost, 127.0.0.1, its 'real' IP address, etc. etc. You may also want to generate the IMG SRC tags using known parameters such as width and height (for the tag itself) and the 'okay' filename (to pass via the querystring). 
 
This method will definitely affect performance, so you will have to measure for your environment and decide whether the tradeoff is acceptable. 
 

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Protecting the images themselves 
 
Now, as we know, it's virtually impossible to prevent people from taking your images when they browse your web site, e.g. saving them to their hard drive and re-using them. While they will always be able to use the PrintScreen button (or one of the many shareware / commercial screen scrapers out there), there are several things you can do to prevent the casual user from using the most common methods: 
 
    Protecting Your Images on the Web